Phacoemulsification is currently the preferred technique used by eye surgeons for cataract extraction involving the removal of the cloudy eye crystalline lens. Through a small incision in the cornea or the sclera (typically 1.5 to 3.2 mm) the cataractous crystalline lens is extracted using a device called a phacoemulsifier and then an artificial intraocular lens is implanted. This lens has the function of replacing the crystalline lens, so that the vision can be restored to the level it was before the cataract appeared.
An early phacoemulsifier can be seen in U.S. Pat. No. 3,589,363 (1971) to Kelman, which is incorporated herein by reference, that comprises a hand piece connected to a cylindrical hollow needle, which has a central bore 1.0 to 1.5 mm in diameter that is introduced inside the eye through the incision previously made. The needle vibrates as a consequence of the ultrasonic energy generated by a source inside the hand piece (usually piezoelectric crystals), which converts electricity, into ultrasonic vibration. The needle emulsifies the cataract converting its substance into very small particles that are aspirated through its central lumen in a controlled manner. The needle, however, is not designed for cutting the nucleus of the cataract or dividing it in several sizable fragments. Also, as the needle produces heat while vibrating, it is covered with a sleeve through which balanced saline solution is flowing. This fluid cools the needle and replaces the fluid being withdrawn from inside the eye, thus avoiding the collapse of the anterior chamber.
The needle involved in many prior art techniques has a cylindrical shape with a diameter between 1.0 to 1.5 mm, and thus is not well suited for cutting or separating the cataract in sizable fragments, which is the preferred approach taken in modern phacoemulsification techniques. In an effort to do so, a technique has been developed which includes sculpting channels or grooves in the surface of the cataract using the cylindrical needle. The grooves must be wider than the needle's diameter so that the cataract may be cracked into four segments (the so called divide and conquer nucleofractis). In order to sculpt grooves in cataracts of a certain hardness level, there is utilized a high power of ultrasonic energy. This has been shown to be able to produce damage to the eye, if applied for a long enough period of time. Moreover, even with the application of high ultrasonic energy levels, the dividing of a very advanced cataract still may not be possible using the method of sculpting grooves, as these cylindrical hollow needles are not really adequate to divide the cataract in sizable fragments by themselves. In an effort to avoid the necessity of sculpting grooves, other surgical instruments have been designed that use mechanical energy to divide the cataract while attempting to save ultrasonic energy. These mechanical devices include choppers and pre-choppers. Many models are available (for instance: Nagahara's chopper available from Rumex Ophthalmic Surgical Instruments, St. Petersburg, Fla., USA—Reference: 7-063 TH) and Akahoshi's pre-chopper (Asico, Westmont, Ill., USA—Reference Universal AE-4282)). These devices use mechanical energy to divide the nucleus. However, phaco chop techniques can be more technically difficult, leading to a greater likelihood of complications, and, moreover, dividing hard nucleus (brunescent and black) cataracts with pre-chopping techniques may be very difficult to master by surgeons.
Currently there are several phacoemulsification devices available (Infiniti Vision System, Alcon Inc., Fort Worth, Tex., USA; Sovereign, Advanced Medical Optics, Santa Ana, Calif., USA; Millennium, Bausch & Lomb, Rochester, N.Y., USA) that use different pumps and different needles. An example of a phacoemulsification device is found in U.S. Pat. No. 6,478,766 assigned to Alcon, Sic. (Hunenberg, CH), which patent is incorporated herein by reference. The Infiniti System phacoemulsification device of Alcon Inc., Fort Worth, Tex., USA has the option of using, in addition to the ultrasound sonic energy, fluid liquefaction of the cataract to help break down the cataract (e.g., see U.S. Pat. Nos. 5,616,120 and 6,676,628 also to Alcon which are incorporated herein by reference). The newer phacoemulsification devices also have the capability of modulating the power of ultrasound applied. In general the manufacturers have designed them to extract the cataract after dividing it into sizable fragments (e.g., four or more) which are then emulsified using cylindrical needles.
U.S. Pat. No. 4,504,264 to Kelman, which is incorporated herein by reference, describes an ophthalmological instrument that features an aspiration needle that is longitudinally vibrated as well as laterally oscillated. The lateral oscillation is described as working in association with the longitudinal vibration movement to promote more rapid fragmentation.
U.S. Pat. No. 6,592,541 to Kurwa, which is incorporated herein by reference, describes and ophthalmological device for cutting a nucleus of a cataract with a phaco tip having a body with a solid blade with a face edge. The device is used alternately with a standard phaco tip (needle with open end) to remove cataracts. As will become more apparent below (e.g., see the Summary of Invention discussion below) the cutting phaco tip, has a design that is not efficient in many respects in the cutting and fragmentizing of the wide range of cataract types faced.
Due to the limitations as to current phacoemulsification surgical instruments available, ophthalmologists around the world rely on basically the same phacoemulsification surgical technique, with some minor variations. The phacoemulsification surgical technique currently relied upon includes the following basic steps:
1. The providing of an access incision which is typically corneal or scleral with a size often varying between 1 and 3.2 mm. The incision may be located superiorly (12 or 11 o'clock positions), or completely temporal. Incision architecture may vary. There may be utilized single plane, two plane or three plane incisions, depending on the surgeon's preference. All of these incisions are intended to be watertight and do not require sutures to close.
2. Capsulorhexis is the surgical step where a central circular portion of the anterior capsule is removed and it leaves the anterior cortex of the cataract exposed. In other words capsulotomy involves creating a continuous tear of the anterior wall to produce a smooth-edged round opening. The continuous tear capsulotomy is known as “capsulorhexis”. Such a capsulotomy facilitates removal of the old lens and also facilitates in-the-bag implantation of an intraocular lens. There are several modes of capsulorhexis forceps and as some examples reference is made to U.S. Publication 2004/0116950 A1 to Elibschitz—Tsimhoni and U.S. Publication 2005/0228419 to El-Mansoury for a discussion of capsulotomy techniques and instruments.
3. Hydrodisection is a maneuver by which, using balanced saline solution injection, the cortex of the cataract is separated from the capsules, so that the cataract can rotate inside the bag.
4. Hydrodelineation is a maneuver by which, using balanced saline solution, the nucleus of the cataract is separated from the most peripheral portion of the cataract that is epinucleus and cortex, so that the nucleus can rotate freely.
5. Nuclear pre-fracture is a more recent cataract surgical technique wherein, before trying to emulsify a cataract, the nucleus is divided into sizable fragments by one of several methods, such as those described above, in order to facilitate its extraction. As noted above, since the phacoemulsification cylindrical needles can emulsify and aspirate just one small portion of the cataract at a time, and not big portions of the cataract, the pre-fracture technique facilitates the complete removal of the cataract material as with a subsequently applied cylindrical phacoemulsification needle. One pre-fracture method involves sculpting deep grooves inside the cataract with the phaco needle to provide for the fragmentation using the needle, and a second instrument to push the fragments apart. The downside of this technique is that it requires more ultrasonic energy, especially in hard and black cataracts, and this high energy level requirement can cause damage to the cornea. Moreover, using this method sometimes it can be impossible to divide certain very hard cataracts (like black cataracts), and it may be necessary to widen the surgical incision to extract it in one piece and then suture it, which is undesirable from a post treatment healing standpoint.
6. Other alternative techniques to divide the cataract before emulsifying it, is using the choppers and the prechoppers (like the above described Nagahara's chopper and Akahoshi's prechopper), which use mechanical energy. They have the drawback of being difficult to learn, taking a long time for the surgeon to master these techniques. Moreover they have the risk of rupture of the anterior capsule edge (in the case of choppers) or zonular stress (in the case of prechoppers). In very hard nucleus (brunescent and black cataracts), these techniques are not easy to perform, even for the experienced surgeon, since the fragments do not separate completely, but their fibers are stretched without breaking.